There has been interest in both making dyes available in liquid formulations and enhancing the water solubility of dyes which dissolve in the dye bath. Approaches to the former object have been concentrated dye solutions in water/organic solvent mixtures and the development of aqueous dye dispersions and one approach to the latter object has been the addition of the tetrasodium salt of ethylene diamine tetra acetic acid (EDTA) or glycine to an ultimately spray dried formulation. There is also interest in enhancing the water solubility, especially the cold water solubility, of dispersed water soluble dyes.
The aqueous dye dispersion approach was proposed for both cationic and anionic dyes in U.S. Pat. No. 3,770,371. Basically, these water soluble dyes are driven out of solution by the addition of selected electrolytes and the dispersion is stabilized by the addition of a dispersant. A modification in which either acid or reactive dyes are driven out of solution by supersaturation of the water dispersion medium which contains suitable anionic dispersants was proposed in U.S. Pat. Nos. 4,110,073 and 4,264,323, respectively. Both of these patents also taught extensive size reduction of the dye particles to be dispersed. Later refinements taught in U.S. Pat. Nos. 4,435,181 and 4,468,230 resulted in dispersions of reactive and acid dyes, respectively, which had commercially attractive low shear viscosities. Another approach taught in European Patent Publication No. 0,123,654 is to replace the anionic dispersants recommended and exemplified in the prior teachings of such dispersions with oligomeric to polymeric ethylene oxide derived non-ionic dispersants. However, the literature dealing with these dispersions seems to have assumed that adequate dye solubility would be observed upon diluting the dispersions shown to the dye concentrations typical of the baths used to apply the dye to the goods to be colored.
There is a need to enhance the rate and extent of solution observed when anionic dye dispersions are diluted for final use. For instance, some nylon fibers used in carpets begin fixing dye at room temperature so that the cold water solubility observed on the dilution of acid dye dispersions is of concern. If the dye does not quickly and completely dissolve, non-uniform dyeings may result. Some areas of the carpet may be deeply colored while others are inadequately colored. Furthermore, in many cases the dye is ultimately fixed by a steam treatment so that heating of the dye bath is conducted only to the extent necessary to fully dissolve the dyes. Therefore, there is also a desire by dyers for dispersions that only require dilution without heating for conversion to solutions. However, because the dye fixation is from a truly dissolved state, the concern is with essentially particle free solutions as opposed to apparent solutions determined by various filtration tests. A convenient test is the visual appearance of the "solution" in a strong light which is hereinafter referred to as "visual solubility".
The concentrated dye solutions of certain anionic dyes has been discussed in U.S. Pat. Nos. 3,963,418 and 4,014,646. In these cases high dye solubility in an aqueous medium is achieved by the use of an organic cosolvent and the avoidance of sodium cations. In the typical production of anionic dyes the water solubilizing group is an acid group neutralized with sodium, but here the sodium is carefully displaced with lithium or ammonium cations. The stability of these solutions to dilution with hard water is assured by the addition of certain carboxylic acid bearing chelating agents to complex or sequester those metal ions such as calcium and magnesium whose presence in hard water causes precipitation of the dissolved dye. In order to avoid introducing sodium ions it is suggested that these chelating agents be added in their free acid forms.
The use of the free acid forms of chelating agents to form metal complex dyes, particularly trivalent chromium complexes, has been discussed in U.S. Pat. No. 3,305,539. Although it is indicated that the chelate enhances solubility, it is readily apparent from the sodium hydroxide neutralization taught in the working examples that this enhanced solubility is associated with the formation of a particular structure complex and not the initial absence of sodium or potassium counterions.
Spray dried dye powder of selected anionic dyes diluted with substantial amounts of an anionic dispersant in which the cold water "solubility" has been enhanced by the addition of tetrasodium EDTA or glycine is disclosed in U.S. Pat. Nos. 4,465,491 and 4,487,610 and European Pat. No. 57,158. The "solubility" is evaluated by the presence or absence of residue on SS 1450 CV filter paper. Evidently, the "solutions" were not optically evaluated for the absence of observable particles. The filter paper is coarse enough to allow the passage of some particles which would be trapped by finer filter paper such as Whatman No. 2. What is actually obtained appears to be a readily "dispersible" powder, i.e. a powder which forms a fine filterable dispersion on addition to limited quantities of cold water.
There does not appear to be a teaching of how to improve the solubility of aqueous dispersions of sodium neutralized anionic dyes. Although replacement of the sodium ctions with lithium or ammonium might appear to be helpful it is undesirably expensive to obtain commercial quantities of many anionic dyes in other than their sodium salt form, and it is not at all clear that either stable dispersions or solutions with acceptable properties could be made with such modified materials. The addition of tetrasodium EDTA has not been found helful in improving the "visual" solubility of such dispersions.
There is thus a need for aqueous dispersions of anionic sodium neutralized dyes in which the dyes readily dissolve upon dilution of the dispersion with cold water to the dye strengths typically encountered in application baths. In particular, there is a need for dispersions wherein dilution to concentrations of about 5 grams per liter or less results in the absence of visible particles of dye in about three minutes or less.